Synthetic bulk element having thin-ferromagnetic-film switching characteristics



Nov. 25, 1969 P. E. OBERG 3,

SYNTHETIC BULK ELEMENT HAVING THIN-FERROMAGNETIC-FILM SWITCHINGCHARACTERISTICS Filed June 16, 1967 2 Sheets-Sheet 1 ION M I INVENTOR32\ L PAUL E. 055% l Nov. 25. 1969 P E. OBERG 3,480,926

SYNTHETIC BULK ELEMENT HAVING THIN-FERROMAGNETIC-FILM SWITCHINGCHARACTERISTICS Filed June 16, 1967 2 Sheets-Sheet 2 Hg. 6 B P INVENTORAUL E. OBE'RG AT EY United States Patent US. Cl. 340-174 9 ClaimsABSTRACT OF THE DISCLOSURE An element that may be utilized as atransformer, or inductor, core or as a bistable memory core comprising aplurality of stacked, magnetizable layers of thin-ferromagnetic-filmsseparated by interstitial layers of insulating material. Themagnetizable layers possess the magnetic property of uniaxial anisotropyproviding an easy axis thereby with adjacent magnetizable layers havingtheir easy axes aligned along two respectively diilerent axes forming amean axis of magnetization M that is intermediate the two axes of thetwo sets, each set formed by the alternate magnetizable layers.Operation as a transformer, or inductor, core is achieved by theapplication and detection of an AC field along a magnetic axis that isorthogonal to the mean axis M operation as a memory core is achieved bythe application of drive fields and detection of switching fields alonga magnetic axis that is parallel to the mean axis M BACKGROUND OF THEINVENTION The invention herein described was made in the course of orunder a contract or subcontract thereunder with the Department of theNavy.

The present invention relates to magnetizable elements comprising aplurality of stacked, magnetizable layers of thin-ferromagnetic-films,each layer possessing singledomain properties and the magneticcharacteristic of uniaxial anisotropy providing an easy axis along whichthe remanent magnetization thereof lies in a first or a second andopposite direction. The term single-domain property may be consideredthe magnetic characteristic of a threedimensional element ofmagnetizable material having a thin dimension that is substantially lessthan the width and length thereof wherein no magnetic domain walls canexist parallel to the large surfaces of the element. The termmagnetizable material shall designate a substance having a remanentmagnetic flux density that is substantially high, i.e., approaches theflux-density at magnetic saturation. It is desirable that each of theseveral thin-ferromagnetic-film layers that make up the magnetizableelement possess such single-domain property whereby singledomainrotational switching of the magnetization M of such magnetizable elementshall be achieved in a manner such as described in the S. M. Rubens etal. Patent No. 3,030,612. Such magnetizable elements may be fabricatedin a continuous vapor deposition process such as disclosed in the S. M.Rubens et a1. Patent No. 2,900,282 and Patent No. 3,155,561. However,such magnetizable elements may be formed by any one of the plurality ofwell-known methods of fabricating magnetizable memory elements within anevacuatable enclosure, e.g., cathodic sputtering.

As a thin-ferromagnetic-film layer possessing singledomain properties islimited in its maximum thickness to the order of 10,000 angstroms A.) itis apparent that the net flux, which is a function of itscross-sectional area, is limited. Accordingly, it is desirable to have amagnetizable element that is capable of operating in a single-domainmanner while providing substantially larger external magnetic fieldsthat, upon the switching or rotation of the elements magnetization M,couple the lines associated therewith producing an output signal thereinthat is of a substantially larger magnitude than that achieved by asingle thin-ferromagnetic-film layer. Prior art arrangements ofmagnetizable elements operating as a single element comprised aplurality of stacked, similar magnetizable layers ofthin-ferromagnetic-films separated by interstitial layers of insulatingmaterial involved all such magnetizable elements wherein the easy axesof all of the thin-ferromagnetic-film layers thereof were aligned.However, in the preferred embodiment of the present invention alternatemagnetizable layers have their easy axes aligned along two respectivelydiflerent axes forming a mean axis of magnetization M that isintermediate the two axes of the two sets of alternate magnetizablelayers.

Prior art arrangements of magnetizable elements operating as a singleelement comprised a plurality of stacked, similar magnetizable layers ofthin-ferromagnetic-film separated by interstitial layers of insulatingmaterial that are fabricated with the easy axes of all magnetizablelayers aligned. However, if it is desired that the magnetizable layersshould rotate in a single-domain manner it is essential that the totalthickness of the magnetizable element be limited to a substantially thindimension. The reason for this is that when the magnetization M in themany magnetizable layers rotates such layers magnetization M vectorsrotate in the same direction. Thus, the components of M that areperpendicular to the major surfaces of the layers are all in the samealigned direction through the thickness thereof tending to be continuousin the magnetizable and insulating layers. In other words, internal polepairs, i.e., pole pairs on opposite surfaces of each insulating layer,tend to cancel out each other leaving only the poles on the top andbottom layers uncancelled. This results in a small demagnetizing field,i.e., the field applied to the magnetizable layer that tends todemagnetize the layers normal magnetization for the large thickness thatis produced by the many magnetizable and insulating layers. This smalldemagnetizing field approaches that of bulk magnetizable material of thesame thickness causing the magnetizable layers to switch in a mannersimilar to bulk material switching.

In contrast to this prior art arrangement, by utilizing the presentinvention the magnetization M in adjacent magnetizable layers rotate inopposite directions whereby the components of M that are perpendicularto the major surfaces of the layers are in opposite, but aligned,directions perpendicular to the thickness of the element. In thisarrangement the internal pole pairs do not tend to cancel out eachother. This results in a very large normal demagnetizing field on eachmagnetizable layer for the large thickness produced by the manymagnetizable and insulating layers. This large demagnetizing fieldforces the magnetization M of the individual magnetizable layers toswitch in a single-domain manner similar to that achieved bymagnetizable elements of a single thin-ferromagneticfilm layer. Whenthis large demagnetizing field is present the magnetization M vectorremains essentially in the plane of the magnetizable layer during itsrotation; this is a requirement and the reason for the high speed changein magnetization provided by single-domain films.

SUMMARY OF THE INVENTION The present invention is an improvement of suchabove discussed prior art arrangements of magnetizable elementscomprising a plurality of stacked, similar magnetizable layers ofthin-ferromagnetic-films that are separated by interstitial layers ofinsulating material. All of the magnetizable layers are of substantiallythe same material and thickness and possess the magnetic characteristicsof single-domain property and uniaxial anisotropy for providing an easyaxis along which the remanent magnetization thereof shall lie in a firstor a second and opposite direction. Alternate magnetizable layersforming a first set of layers are formed with their easy axes alignedalong a first axis with the interstitial magnetizable layers forming asecond set of layers with their easy axes aligned along a second axisthat is different from the first axis. Thus, there are formed first andsecond sets, each of a plurality of magnetizable layers, with their easyaxes at an angle forming a mean magnetization axis M that substantiallybisects the acute angle formed by the easy axes of the two sets.

The magnetizable elements of the present invention have the ability tobe operated as a transformer, or inductor, core or as a bistable memorycore. Operation as an inductor core is achieved by the application anddetection of an AC field along a magnetic axis that is orthogonal to themean magnetization axis M Operation as a bistable memory core isachieved by the application of a drive field and the detection of aswitching field along a magnetic axis that is parallel to the meanmagnetization axis M Drive and sense lines, or windings, that aremagnetically, or conductively, coupled to the magnetizable elements ofthe present invention may be of the Well known printed circuit type asparticularly adapted in bistable memory core operation or moreconventional transformer winding techniques when operated as an inductorcore. Additionally, readout may be by any of the well known methods,such as magnetoresistive or magnetooptic. Accordingly, it is a primaryobject of the present invention to provide a magnetizable element thatmay be utilized as an inductor core or as a bistable memory core that iscomprised of a plurality of stacked, magnetizable layers ofthin-ferromagnetic-filrns separated by interstitial layers of insulatingmaterial forming an element of substantial thickness while yetpermitting the individual, and collective magnetizable layers to rotate,or switch, in a single-domain manner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of amagnetizable element of a plurality of magnetizable layers separated byinterstitial layers of insulating material as proposed by the presentinvention.

FIG. 2 is a plan view of the magnetizable element of FIG. 1 illustratingthe orientation of the two easy axes of the respectively associated setsof magnetizable layers of the magnetizable element of FIG. 1.

FIG. 3 is a schematic illustration of the related vectors involved withthe switching mechanism of adjacent magnetizable layers as proposed bythe present invention.

FIG. 4- is a plan view of a magnetizable element of the presentinvention illustrating the orientation of the easy axes M and M of therespectively associated two sets of magnetizable layers of FIG. 1 whenutilized as a transformer element.

FIG. 5 is a plan view of a magnetizable element i1- lustrating theorientation of the two easy axes M and M of the respectively associatedtwo sets of magnetizable layers of FIG. 1 when utilized as a memoryelement.

FIG. 6 is a composite illustration of the hysteresis loopcharacteristics of the magnetizable elements of FIG. 4 and FIG. 5.

FIG. 7 is an illustration of another embodiment of the present inventionin which the magnetizable element is comprised a plurality of stacked,magnetizable layers having a washer-like configuration.

FIG. 8 is an illustration of another embodiment of the present inventionin which the magnetizable element is comprised of a plurality ofconcentric, different-diameter toroidal-shaped magnetizable layers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS W t pa ic lar refe ence t FIG.1 t e e s i lustrated .4 a side view of a magnetizable element thatincorporates the inventive concept of the present invention.Magnetizable element 10 is comprised of a substrate 12 and a pluralityof magnetizable layers 14, 16 insulatively separated by a plurality ofinsulating layers 18. Magnetizable element 10 is particularly adaptableto be fabricated in successive deposition steps of alternate layers ofmagnetizable material and insulating material in an evacuatableenclosure. Magnetizable layers 14, 16 are thin-ferromagnetic-film layersthat possess the magnetic characteristics of single-domain propertiesand uniaxial anisotropy for providing an easy axis along which theremanent magnetization thereof shall lie in a first or a second andopposite direction. Each of the several thinferromagnetic-film layers14, 16 that make up the magnetizable element 10 possess suchsingle-domain property whereby single-domain rotational switching of themagnetization M of each of such layers may be achieved in the mannersuch as described in the S. M. Rubens Patent No. 3,030,612.Additionally, magnetizable element 10 is preferably fabricated in acontinuous vapor deposition process such as disclosed in the S. M.Rubens et a1. Patent No. 2,900,282 and 3,155,561 or the A. V. PohmPatent No. 3,065,105. The multi-layer element 10 may be deposited upon asubstrate 12 of many well known materials such as glass or metal.

With particular reference to FIG. 2 there is illustrated a plan view ofthe magnetizable element 10 of FIG. 1 for purposes of illustrating theorientation of the easy axes M and M each respectively associated withthe two associated sets of layers; one set formed by the alternatelayers 14a, 14b, 14c, and 14d, and the other set formed by the alternatelayers 16a, 16b, 16c, and 16d as illustrated in FIG. 1. The two sets ofdifferent alternate magnetizable layers 14, 16 have the respectivelyassociated easy axes M M separated by an acute angle oz. These easy axesM M are separated by an acute angle cc forming an effective, average, ormean easy axis M which preferably forms an angle a/2 with each of theaxes M M For purposes of the discussion in the present application themean or average easy axis M shall be defined as the easy axis bisectingthe acute angle formed by the two axes M M that are associated withtheir respective sets of magnetizable layers 14, 16; it being recognizedthat the obtuse angle /3 established by the two easy axes M Mestablishes a second mean easy axis that is orthogonal to the abovedefined mean easy axis M Thus, in summary it may be stated thatmagnetizable element 10 is basically comprised of two sets of stacked,superposed, magnetizable layers (14, 16 in which adjacent magnetizablelayers are separated by an insulating layer (18). All layers of each sethave their easy axes (easy axes M of the first set of magnetizablelayers 14, and easy axis M of the second set of magnetizable layers 16)aligned with the two respective easy axes of the two sets (easy axes Mand M of sets one and two, respectively) oriented at an acute angle (a)forming an effective or mean easy axis (M that bisects the so-formedacute angle. Note: for ease of discussion, the vector magnetization M,either aligned along, or rotated out of alignment with, the associatedeasy axis, and the associated easy axis M shall be identified by similarterms; i.e., magnetization M, of layer 14 having an easy axis M Withparticular reference to FIG. 3 there is presented a diagrammaticillustration of the paths traced out by the magnetization vectors ofmagnetizable layers 14, 16. As discussed above, the present inventionrelates to a magnetizable element that comprises a plurality of stacked,superposed, magnetizable layers of thin-ferromagnetic-films separated byinterstitial layers of insulating material. The magnetizable layerspossess the magnetic property of uniaxial anisotropy providing an easyaxis thereby with alternate magnetizable layers having their easy axesaligned along two respectively different axes M and M forming a meanaxis of magnetization M,

that is intermediate the two axes of the two sets of alternatemagnetizable layers. Each of the layers of magnetizable material, suchas adjacent layers 14, 16, possess single-domain properties that arecapable of having their magnetization switched, or rotated, in asingle-domain manner such as disclosed in the above referenced S. M.Rubens et al. Patent No. 3 ,030,612.

If the magnetization M as in magnetizable layer 16, is effected by anapplied drive field H along the mean axis M the magnetization M isinduced to rotate in the direction away from the applied drive field Htoward a position M through an angle When the magnetization begins torotate out of alignment with its easy axis M there is generated acomponent M that is normal to the plane of the magnetizable layer.However, the demagnetizing field of the magnetizable layer 16 limitsthis normal component to extremely small values causing themagnetization M to rotate through path 30 which path is substantially inthe plane of layer 16. This mechanism is more fully discussed in thetext Amplifier And Memory Devices: With Films and Diodes McGraw-HillBook Company, 1965, Chapter 13.

With a plurality of magnetizable layers 16 arranged in a stacked,superposed arrangement similar to that of FIG. 1 with the easy axis ofall such layers 16 aligned, an applied drive field H would cause themagnetization M of all such layers 16 to rotate in the same direction.Thus, the components M that are perpendicular to the major surfaces oflayer 16 are all in the same aligned direction through the plurality oflayers tending to be continuous therethrough. In other words, theseadjacent layers 16 would form internal pole pairs with respect toadjacent layers 16, such as components M that tend to cancel each otherleaving only the poles on the top and bottom layers 16 uncancelled. Thisresults in a very small demagnetizing field M for the relatively largethickness through the plurality of layers 16, this very smalldemagnetizing field approaches that of bulk magnetizable material of thesame thickness causing the magnetization of the plurality ofmagnetizable layers 16 to switch in a manner similar to that of bulkmaterial.

However, if instead of the above, wherein there was provided a pluralityof stacked layers 16 having their easy axes aligned, assume that thereare provided a like number of magnetizable layers 14 interstitial withthe layers 16 forming adjacent pairs of layers 14 and 16 and furtherassume that the easy axes of such layers 14 are aligned but at an anglea with the aligned easy axes of the plurality of layers 16. Theseadjacent pairs of layers 14, 16 may then be assumed to generate aneffective, or mean, magnetization axis 32 which bisects the angle orbetween the easy axes M M associated with layers 14, 16 respectively.Now, if a drive field H is appliedparallel to the planes of the layers14, 16 and of an opposite polarization with respect to the averagemagnetization M,, along the mean axis 32 the magnetization M and M oflayers 14 and 16, respectively, are forced to rotate in oppositedirections. Thus, as in the example shown in FIG. 3, magnetization M oflayer 14 would rotate in a clockwise direction (as viewed from above)along a path 34 while magnetization M in layers 16 would rotate in acounterclockwise direction along path 30. The vertical components M andM generated by the rotation of magnetization M and M of layers 14 and16,'respectively, due to the opposite directions of rotation, would beof substantially equal magnitude but of opposite polarity. Thus, byutilizing the inventive concept of the present invention themagnetization in the adjacent magnetizable layers 14 and 16 rotate inopposite directions whereby the components of M that are perpendicularto the major surfaces of the layers are in opposite, but aligned,directions through the thickness of the magnetizable element provided bythe plurality of pairs of layers 14, 16 and the associated insulatinglayers 18see FIG. 1. In this arrangement the internal pole pairs, i.e.,the M components M and M that are perpendicular to the major surfaces ofthe layers 14 and 16, do not tend to cancel out each other. This resultsin a very large demagnetizing field for the large thickness produced bythe many magnetizable layers 14, 16 and insulating: layers 18. Thislarge demagnetizing field forces the magnetization M of the individualmagnetizable layers 14, 16 to switch in a single-domain manner similarto that achieved by magnetizable elements of a singlethin-ferromagnetic-film layer. When this large demagnetizing field ispresent the magnetization M vector of each layer 14, 16 remainsessentially in the plane of the associated magnetizable layer 14, 16;this is a requirement and the reason for high speed rotational change inmagnetization.

With particular reference to FIG. 4 there is illustrated a plan view ofa magnetizable element 10a illustrating the orientation of the easy axesM M formed by the two sets of magnetizable layers 14, 16 respectively,when magnetizable element 10 is to be utilized as a transformer core.Although the illustrated embodiment is discussed as magnetizable it isto be understood that this is not essential thereto. A permeable layerhaving a permeability greater than that of air and with substantially noremanent magnetization could function as a transformer, or inductor,core. In this arrangement, utilizing magnetizable element 10a as atransformer, or inductor, core the easy axes of the two sets ofmagnetizable layers 14, 16 are established along the respective easyaxes M M generating a mean easy axis M that bisects the acute angletherebetween. Operation of magnetizable elements 10a as a transformer,or inductor, core is achieved by the application and detection of an ACfield along a magnetic axis that is orthogonal to the mean axis M The ACmagnetizing field :H applied along axis 40 by winding 42 causes themagnetization associated with axes M M to oscillate about the mean axisM through the respective angles e5 Q. The flux variations ofmagnetizable element 10 due to the oscillation of the magnetizationthereof about its mean axis M is detected by winding 44; as an inductorcore only one winding 42 is required. In this arrangement windings 42and 44 function as the primary and secondary windings, respectively,that are inductively coupled to the magnetizable element 10a. By winding42 coupling a magnetizing force i-H of an intensity (H H just sufiicientto cause the magnetizations M M to oscillate :45 about the mean axis Mi.e., equal to the total flux change in magnetizable element 10a isequal to approximately 0.7 of the total switchable flux therein.

With particular reference to FIG. 6 there is presented the BH loop 60that is an approximate representation of the magnetic flux pathtraversed by the magnetic flux of magnetizable element 10a when operatedin the transformer mode as described with particular reference to FIG.4. Loop 60 represents the substantially lossless operation ofmagnetizable element 10a such as is usually associated with theoperation of thin-ferromagnetic-film layers when driven in the harddirection. As will be further discussed with particular reference toFIG. 5, loop 62 represents the approximate path traversed by themagnetic flux of element 1012 when operated as a memory element inaccordance with the embodiment of FIG. 5. Loops 60 and 62 of FIG. 6 aretypical BH loops of thinferromagnetic-film elements having uniaxialanisotropy and being driven in the hard and easy directions,respectively. For a detailed discussion of the rotational loops of FIG.6 reference may be had to the publication Thin Ferromagnetic Films, A.C. Moore, IRE Transactions on Component Parts, March 1960, pages 3-14.

With particular reference to FIG. 5 there is illustrated a plan view ofa magnetizable element 10b when utilized as a memory element. Operationas a memory element, or bistable core, is achieved by the application ofa drive field :H, where +H may be representative of the storing of a 1and H may be representative of the storing of a O in memory element101). This drive field H is coupled to memory element b 'by means ofcoil 52 providing a drive field that is oriented parallel to the meanaxis M,,. In this embodiment the applied drive field H is of anintensity in the area of magnetizable element 101), approximating Hcausing the magnetizations M and M to completely switch, i.e., berotated a full 180 to assume a magnetization polarization along theirrespective easy axes M and M that is opposite to that of their originalpolarizations. The magnetic flux change in magnetizable element 1% dueto the switching, or not switching of the magnetization M M is detectedby the output, or sense, coil 54 whose magnetic axis is orientedparallel to the mean axis M of magnetizable element 1% inducing a signaltherein that is representative of the informational state ofmagnetizable element 1012 when operated as a memory core. As an example,with the magnetization of the two sets of magnetizable layers 14, 16 ofmagnetizable element 10b established in their respective easy axisdirections M M which directions may be representative of the storage ofa 1 therein, the application of a H-H drive field by winding 52 wouldcause the magnetizations M M thereof to switch 180 reversing theirpolarization and thus inducing a substantial signal in output winding54. Conversely, with the magnetizations of magnetizable layers 14, 16 ofmagnetizable element 1012 established along their easy axes M M theapplication of a-t-H drive field by winding 52 would induce aninsubstantial signal in output winding 54 that may be representative ofthe storing of a O therein.

With particular reference to FIG. 6 there is illustrated the loop 62that describes the magnetic flux path traversed by the magnetic flux ofmagnetizable element 10b when operated as a memory core in accordancewith the embodiment of FIG. 5. It can be seen that loop 62 has asubstantially rectangular form that approaches the ideal characteristicfor a magnetizable memory element.

With particular reference to FIG. 7 there is presented anotherembodiment of the present inventi n that is particularly adapted tofunction as a transformer, or inductor, core such as previouslydiscussed with particular reference to FIG. 4. Magnetizable element 70is comprised of a plurality of stacked, superposedthin-ferromagnetic-film layers 74a, 76a, 74b, 76b similar to the layers14, 16 of FIG. 1. Adjacent magnetizable layers are separated by suitableinsulating layers as in FIG. 1, but are not illustrated for purposes ofclarity. However, in this embodiment each of the magnetizable layers isin the form of a washer providing a closed flux path around the centralaperture for the magnetizing field :H that is applied to magnetizableelement 70 by input winding 72. Layers 74, 76 are fabricated so as tohave radial easy axes that are orthogonal to the :H closed flux path.Adjacent cores, such as cores 74a and 76a provide substantially closedflux paths in a radial direction therebetween whereby there are providedtwo substantially orthogonally closed flux paths by each of two adjacentcores. Application of the AC drive field by means of winding 72 forcesthe magnetization M M of layers 74, 76, respectively, to oscillate abouttheir radially aligned easy axes in the nature as discussed with respectto FIG. 4 whereby there is produced by layers 74, 76 a magnetic fluxchange which is in turn coupled to output winding 78. As with respect tothe embodiment discussed with respect to FIG. 4 windings 72 and 78function as the primary and secondary windings, respectively, oftransformer core 70; as an inductor core only winding 72 is required.The magnetic flux change in core 70 traverses a BH loop similar to thatof loop 60 as discussed with particular reference to FIG. 6.

With particular reference to FIG. 8 there is presented anotherembOdiment of the present invention that is particularly adapted tooperate as a memory core in the nature as discussed with particularreference to FIG. 5. Magnetizable element is comprised of a plurality ofconcentric rings of thin-ferromagnetic-films with adjacent layersseparated by suitable insulating layers as in FIG. 1, but notillustrated herein for purposes of clarity. In this embodiment themagnetization of rings 84, 86 are aligned in opposite directions thatare substantially parallel to the major axis 81. The concentric rings84, 86 provide closed flux paths for the iH drive field coupled theretoby input winding 82. Additionally, the magnetization M M of adjacentlayers 84, 86 are provided substantially closed flux paths through suchadjacent rings. As is discussed with particular reference to theembodiment of FIG. 5, application of the :H drive field to magnetizableelement 80 by input winding 82 causes the magnetization M M of layers84, 86, respectively, to rotate out of alignment with their easy axesand to become aligned in a first or second and opposite direction alonga line substantially parallel to the major axes 81.

Thus it is apparent there has been described and illustrated herein apreferred embodiment of the present invention that provides an improvedmagnetizable element comprising a plurality of stacked, magnetizablelayers of thin-ferromagnetic-films that operate in a single-domainmanner.-It is understood that suitable modifications may be made in thestructure as disclosed provided that such modifications come within thespirit and scope of the appended claims. Having, now, fully illustratedand described my invention, what I claim to be new and desire to protectby Letters Patent is set forth in the appended claims.

What is claimed is:

1. A synthetic bulk element operated in a domain rotational mode,comprising:

a plurality of stacked, superposed layers of substantially similarphysical dimensions, material composition and magnetic characteristicseach layer having a permeability greater than one, adjacent ones of saidlayers being separated by an insulating material;

each of said layers possessing the magnetic characteristic ofsingle-domain property and having a preferred axis of magnetizationalong which the magnetization thereof may lie;

said layers arranged in first and second sets;

said first set formed by alternate ones of said layers having theirpreferred axes aligned along a first axis M said second set formed byalternate ones of said layers,

interstitial those of said first set, having their preferred axesaligned along a second axis M for forming an angle at with said firstaxis M a mean easy axis M formed by said first axis M and said secondaxis M and bisecting said angle or;

input means inductively coupling a drive field to said layers along saidaxis M said drive field causing the magnetization of said first andsecond sets to rotate in a domain rotational manner in oppositerotational directions;

equal but opposite polarity field components M and M normal to theplanes of adjacent layers of said first and second sets formed by saidrotating magnetization;

internal pole pairs formed by said field components M and M cancellingeach other except at the top and bottom one of said layers for forming arelativley small demagnetizing field for the relatively large thicknessof the stacked layers.

2. The element of claim 1 wherein said layers are magnetizablethin-ferromagnetic-fil-ms and said preferred axes are easy axes due touniaxial anisotropy.

3. The element of claim 2 wherein the adjacent layers of the first andsecond sets form substantially closed flux paths for each other.

4. A bistable memory operable in a domain rotational mode, comprising:

a plurality of stacked, superposed ma gnetizable thin-.ferromagnetic-film layers of substantially similar physical dimensions,material composition and magnetic characteristics separated byintersitial layers of insulating material;

each of said magnetizable layers possessing the magnetic characteristicsof single-domain property and of uniaxial anisotropy providing an easyaxis along which the remanent magnetization thereof may lie in a firstor a second and opposite direction;

said magnetizable layers arranged in first and second sets;

said first set formed by alternate ones of said magnetizable layershaving their easy axes aligned along a first axis M said second setformed by alternate ones of said magnetizable layers, other than thoseof said first set, having their easy axes aligned along a second axis 2;

said first and second axes M and M forming an angle a therebetween forproviding a mean axis M input and output means inductively coupled tosaid magnetizable layers having a magnetic axis that is parallel to saidmeans axis M said input means coupling a drive field H to said layersfor causing the magnetization of said first and second sets to rotate inopposite directions about the mean axis M for providing a signal to saidoutput means, and for establishing the magnetization of said first andsecond sets in a first or a second and opposite direction along theirrespective first and second axes M and M equal but opposite polarityfield components M and M normal to the planes of adjacent layers of saidfirst and second sets formed by said rotating magnetization;

internal pole pairs formed by said field components M and M cancellingeach other except at the top and bottom ones of said layers for forminga relatively small demagnetizing field for the relatively largethickness of the stacked layers.

5. The memory of claim 4 wherein said first and second axes M and M forman acute angle or therebetween for providing said mean axis M thatbisects said acute angle.

6. The memory of claim 5 wherein said mean axis M bisects said acuteangle on in equal portions 11/2.

7. The memory of claim 6 wherein said drive fieldI-I is of an intensity,in the area of said layers, H H of said layers.

8. The memory of claim 7 wherein said input and output means includeseparate associated windings.

9. The method of operating a synthetic bulk element in a domainrotational mode, comprising:

forming a plurality of stacked, superposed layers of substantiallysimilar physical dimensions, material composition and magneticcharacteristics, each of said layers having a permeability greater thanone;

generating in each of said layers the magnetic characteristics of singledomain property and uni-axial anisotropy providing an easy axis alongwhich the remanent magnetization thereof may lie in a first or a secondand opposite direction;

arranging said layers in first and second sets, alternate layers formingsaid first set and the layers that are interstitial the alternate layersof said first set forming said second set;

orienting the easy axes of the layers of the first set along a firsteasy axis M orienting the easy axes of the layers of the second setalong a second easy axis M forming an angle or between said axes M and Mforming a mean easy axis M betweensaid axes M and M and bisecting saidangle a;

coupling a drive field to said layers along said axis M rotating themagnetization of the layers of said first and second sets in a domainrotational mode in opposite rotational directions and substantially inthe planes of the layers;

generating equal but opposite polarity field components M and M normalto the planes of adjacent layers of said first and second sets;

forming internal pole pairs with respect to field components M and M ofadjacent layers;

cancelling all internal field components M and M leaving uncancelledonly those poles on the top and bottom layers.

References Cited UNITED STATES PATENTS 3/1963 Rubens 340l74 3/1968Feldtkeller 340---174 XR OTHER REFERENCES BERNARD KONICK, PrimaryExaminer G. M. HOFFMAN, Assistant Examiner

